C++ Library to infaceface with StreamDeck devices

This library is written to mirror the Python library with similar goal. To integrate into non-Python projects a C++ interface library is better, though.

The interface is minimal so far. It can be extended. There is no program code yet which takes advantage of the library, just an example program that is used to test the code in the package.

Interface

Using the library is simple. The streamdeck::context object can be instantiated once and only takes a path argument. This argument is only used in the ImageMagick routes which are used behind the scenes. To handle USB devices libhidapi-libusb is used which will create several threads and in general might prevent others users from using the opened devices concurrently. This is expected. It means, though, the library has an internal state and it is not possible, in general, to have multiple objects of type streamdeck::context in use at the same time.

The constructor can fail if the USB library fails to initialize. If no devices are found the constructor will succeed. The found devices, if any, can be iterated over with the usual C++ interfaces: begin, end, empty. Only devices which can be handled by the library are reported. This might mean that new devices might not be handled (yet).

To distinguish the devices their serial numbers can be used:

streamdeck::context ctx(argv[0]);
for (auto& dev : ctx)
  std::cout << dev->get_serial_number() << std::endl;

If more than one device is reported but only one is needed the others should be closed with a call to the close member function.

The set_key_image member function allows to set an image for a key. One variant take a file name in which case the ImageMagick libraries are used to transform the image as required by the device. The image will be scale and transformed, if necessary, and converted to the right format. Theoretically it is even possible to use SVG files but the handling of this type of files at least for now does not work correctly. Better use a bitmap format, lossless or lossy.

The second variant allows to pass an Magick::Image object, as constant reference or a rvalue. This allows to generate the image on-the-fly before displaying it.

The third variant of the interface take an container with the image data stored in it. In this case the library only takes care of the transport of the data to the device. The caller is responsible to provide the data in the correct format.

To read the state of the device the read member function should be used. There is no descriptor-based interface which can be used with epoll etc. This could be constructed with a helper thread and a pipe. The provided read interface returns a vector with the current state of the button after a change. I.e., the read interface is delayed until a button a pressed or released. The read variant with a timeout
parameter returns an optional object which, in case the timeout is reached, contains nothing.

Using the library

As for other package following the accepted guidelines, use pkg-config to determine the command line parameters to pass to the compiler:

$ g++ -c $(pkg-config --cflags streamdeckpp) -o sduser.o sduser.cc

For linking use

$ g++ -o sduser sduser.o $(pkg-config --libs streamdeckpp)

Note: when linking statically one has to pass --static to pkg-config.

Quirk

The firmware on the StreamDeck handles black-and-white images used for the buttons differently. Instead of filling the full button only a half-high image is used, duplicated horizontally to fill the width. Under this the last full color image that was uploaded is used.

If this is not desired then imagine should contain at least one colored pixel.